What is W-OFDM?
W-OFDM (Windowed OFDM) is a variant of CP-OFDM that applies a time-domain window function to each OFDM symbol to reduce spectral sidelobes and improve out-of-band emission performance. By smoothing the sharp transitions at symbol boundaries, W-OFDM significantly reduces spectral leakage into adjacent channels while maintaining backward compatibility with standard OFDM receivers. W-OFDM is effectively the approach adopted by 5G NR, which specifies optional time-domain windowing/filtering at the transmitter.
How Does W-OFDM Work?
In standard CP-OFDM, the rectangular symbol window creates high sidelobes (approximately -13 dB first sidelobe). W-OFDM extends the symbol duration slightly beyond the CP to create overlapping regions between consecutive symbols, then applies a smooth roll-off window (raised-cosine, Hann, Tukey, etc.) to these overlap regions. This smooth transition reduces sidelobes by 10–30 dB compared to rectangular windowing. The overlapping portions of adjacent symbols are added together (overlap-and-add), maintaining the total symbol rate. The receiver can use standard FFT-based OFDM processing with minimal performance impact. 5G NR implementations typically apply W-OFDM-style windowing to reduce OOB emissions without specifying it as a mandatory standard — it is left as a transmitter implementation choice.
Use Cases
5G NR transmitter OOB emission reduction, mixed-numerology operation with reduced inter-numerology interference, spectrum coexistence with adjacent systems, dynamic spectrum sharing (DSS) between LTE and NR, and ACLR improvement without external filtering.
3GPP / Standards Reference
3GPP TS 38.211 (NR physical channels — implementation note on windowing), 3GPP TR 38.802 (NR waveform study)
Related Terms
OFDM | CP-OFDM | P-OFDM | UF-OFDM | FBMC
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